The present invention relates to a boat propeller transmission comprising an input shaft intended to be connected to an output shaft from a drive installation, an intermediate shaft driven by said input shaft via a first bevel gear set, at least one propeller shaft driven by said intermediate shaft via a second bevel gear set, a reversing mechanism for reversing the rotational direction of the propeller shaft relative to said input shaft, and a planetary gear set, providing at least two different gear speeds in the same direction between the input shaft and the propeller shaft.
Boat propeller transmissions, e.g. in propeller drives of the type which are steerably and tiltably mounted on the outside of a boat transom and which are drivably coupled to an inboard engine, usually have only a reversing transmission for reversing the rotational direction of the propeller shaft. Recently, however, two-speed propeller drives have been developed primarily for achieving more rapid acceleration so that the boat will more rapidly reach the planing position for better fuel economy. In boats with turbo-charged diesel engines, the poor charging capacity of the turbo unit at low engine rpm has been compensated with a displacement compressor, which is mechanically driven by the engine and which is coupled in series with the turbo compressor and supercharges in the low rpm range of the engine, but which is disconnected as soon as the charging capacity of the turbo compressor exceeds the charging capacity of the displacement compressor. In this manner, rapid acceleration is achieved, so that the planing position can be rapidly reached. With a two-speed propeller drive unit with a low gear and a direct gear, the engine in low gear reached earlier the rpm at which the turbo compressor charges efficiently, which provides more rapid acceleration and earlier planing over a single speed transmission. With a two-speed drive unit it is possible in a boat with an engine only turbo-charged, to achieve approximately the same performance as a boat with a single speed drive unit and an engine with both a turbo compressor and a displacement compressor. The cost of manufacturing a propeller drive unit with an extra gear speed is, however, significantly lower than the extra cost for the displacement compressor installation.
The purpose of the present invention is to achieve a boat propeller transmission of the type described by way of introduction, with a planetary gear set in a compact and simple design, so that the planetary gear set, when used in an outboard drive, for example, can be placed in the drive leg, maling it possible with a minimum of modification of a single speed drive, to develop it to a two-speed drive.
This is achieved according to the invention by virtue of the fact that the planetary gear set (9) has a gear set housing and a sun gear, which is lockable relative to the housing by means of a releasable one-way clutch, which strives to lock the sun gear upon rotation of a shaft of the planetary gear set in one direction and to release the sun gear upon rotation of the shaft in the opposite direction, and that disengagement means are coordinated with the one-way clutch to permit selective disengagement of the one-way clutch for releasing the sun gear when the shaft rotates in said first mentioned direction.
A preferred embodiment of the transmission according to the invention is characterized in that the planetary gear set has a sun gear which is non-rotatably joined to a sleeve element, which is mounted concentrically with said last mentioned shaft and has an external thread in engagement with an internal thread of a bore in a clutch element, which has an external conical frictional surface which, upon axial displacement of the clutch element, is displaceable into or out of engagement with a facing conical surface of a housing element, that the thread is so formed in relation to the rotational said last mentioned shaft when driving forwards, that the frictional surface of the clutch element is pressed against the frictional surface of the housing upon turning of the sleeve relative to the clutch element, and that hydraulic disengaging means are arranged to displace the clutch element, so that its frictional surface is moved out of engagement with the facing frictional surface.
Such a clutch for locking the sun gear of the planetary gear set is particularly suitable for vertical mounting, for example, in the rig of an outboard drive, by virtue of the fact that the clutch element will then be loaded axially by gravity, which can be used to initially move the frictional surfaces into engagement with each other, and that the engaging force will then be increased by the thread engagement. Only disengagement need be effected by force, while the engagement can occur automatically when the hydraulically operated means are deactivated. In a preferred embodiment of a transmission according to the invention, the clutch element itself is also a piston element in a cylinder, which results in a very simple and compact design.